In recent years, the development of a display device represented by a liquid crystal display device and an organic electroluminescence display device is progressing in order to improve visibility and color reproducibility. Generally, the screen of a display device is formed by a plurality of pixels, and one pixel is formed by three subpixels each arranged with display elements corresponding to red, green and blue which are the three primary colors of light. In this way, the display device is capable of color display. For example, there is a method of increasing the number of primary colors used for display from three to four or more in the conventional method as a method of improving color reproducibility.
In the case when the number of primary colors used for a display is four, an input image signal of three primary colors is converted into an output image signal of four colors and then an image is displayed on a display device.
For example, a display device has been developed in which an image in which an input image signal is converted into two pixels of three primary colors and an output image signal is converted into one pixel of four colors is displayed.